The invention relates to a means of articulation between two connection pieces and a ground connection device for a motor vehicle wheel, particularly a steered wheel, including a piece for connecting to the hub carrier which carries the hub of the wheel of the vehicle and a piece for connecting to the steering link or to the wishbone of the suspension, these two connection pieces being articulated together by this means of articulation.
In the known state of the art, these two pieces are articulated by means of a ball joint. This ball exhibits friction, which introduces resistance to turning into the steering and introduces excessive elastic stress into the steering column. What is more, a ball joint does not perform any filtering, and this may contribute to vibration being allowed to be transmitted back up through the steering wheel.
When the ground connection is of the MacPherson type, it includes a strut mounted between the hub of the wheel and the body of the vehicle, and a coil spring mounted between a lower spring plate secured to the body of the strut and an upper spring plate secured to the rod of the strut.
In ground connections of the Mac Pherson type for steered wheels, a thrust ball bearing is mounted between the upper spring plate and the suspension tower of the vehicle. This thrust ball bearing also, when the steering is turned, has a threshold resistance to rolling, which results in a torque threshold which is undesirable in terms of the feel through the steering wheel.
There is already known, as a replacement for ball joints, a means of articulation which consists of a spider comprising two mutually perpendicular shafts each defining an axis of rotation, each shaft being borne by a connecting piece with the interposition of an elastic articulating ring capable of being stressed in torsion about the axis of rotation of the associated shaft. However, such a means of articulation has an angular displacement which is limited by the relatively poor ability of the elastic articulating ring to tolerate deformation without being damaged or without offering excessive resistance. This may lead to damage to the elastic articulating rings, particularly when the steering link is turned through a large angle.
The object of the invention is to propose a means of articulation in which the permissible angular displacement is greater.
Another object of the invention is to propose a means of articulation which improves the acoustic comfort, for example by reducing the vibration traveling back up through the steering wheel and by reducing the points of contact with the wheel.
Yet another object of the invention is to improve the known technique by eliminating the threshold resistance to turning and by supplying a means of articulation, the angular displacements of which are approximately proportional to the efforts involved in keeping the wheel on course.
To this end, the subject of the invention is a means of articulation between two connecting parts, the said means of articulation comprising an articulation yoke equipped with two non-parallel arms each defining an axis of rotation and each borne by a respective one of the two connecting pieces, with the interposition of elastic articulating rings which can be stressed in torsion about the axis of rotation of the associated shaft, characterized in that the said articulation yoke has at least one bore for the passage of a first shaft with the interposition of at least one elastic articulating ring which can be stressed in torsion about the axis of rotation (known as the xe2x80x9cfirst axis of rotationxe2x80x9d) of the said first shaft so that the permissible relative angle of displacement between the connecting pieces about said first axis of rotation is the sum of the permissible angular displacement of said connecting piece with respect to said first shaft and of the permissible angle of displacement of said first shaft with respect to the articulation yoke.
Advantageously, the means of articulation includes at least one elastic articulating ring between the aforementioned bore and said first shaft and at least one separate elastic articulating ring between said first shaft and said connecting piece which bears it.
Because there are two separate elastic rings, one connecting the yoke to the first shaft and the other connecting the first shaft to the connecting piece, each of the rings works in isolation and is stressed uniformly. If use were made of just one elastic ring, part of which were connected to the yoke and another part of which were connected to the connecting piece, in the region between these two parts, the elastic ring would experience high stresses, because it would be the site of circumferential stresses in opposite directions.
In a first embodiment, the aforementioned two axes of rotation are concurrent and the articulation yoke has two coaxial journals which extend one on each side of said bore to define the second shaft of the means of articulation, said second shaft defining the second axis of rotation, the permissible angular displacement of any one of the connecting pieces about said second axis of rotation being the permissible angular displacement of said connecting piece with respect to the articulation yoke. In this case, there would be far more angular displacement about the first axis of rotation than about the second axis of rotation, for example there would be approximately twice as much. However, this means of articulation is particularly compact, by virtue of the fact that the axis of rotation are concurrent.
In another embodiment, the aforementioned two axes of rotation are not concurrent and the articulation yoke has a second bore for the passage of the second shaft with the interposition of at least one elastic articulating ring which can be stressed in torsion about the second axis of rotation associated with said second shaft, the first bore of the articulation yoke having no intersection with the second bore.
According to another feature, each elastic articulating ring consists of two coaxial tubular parts, between which an elastomeric material of low elastic modulus is molded. As a preference, the elastomeric material has a footprint on the radially interior tubular part which is longer than its footprint on the radially exterior tubular part so that the elastic ring exhibits an approximately constant shear stress, the elastic ring having an approximately constant cylindrical area regardless of its radius, by virtue of the approximately trapezoidal shape of said ring in axial section.
Advantageously, the elastic ring is chosen in such a way as to allow an angular displacement of the order of xc2x120xc2x0 by torsional deformation of the elastic ring.
Advantageously, each connecting piece is shaped like a clevis block, the two branches of each clevis block taking, with the interposition of at least one elastic articulating ring, the ends of a shaft of the articulation yoke.
The invention is also aimed at a ground-connection device for the steered wheel of a motor vehicle, comprising a wheel hub carrier equipped with the aforementioned means of articulation, characterized in that a first connecting piece is secured to the wheel hub carrier, while the second connecting piece is secured to a steering linkage, the first axis of rotation extending approximately in a vertical direction and the second axis of rotation extending approximately in the longitudinal direction of the vehicle.
Another subject of the invention is a ground-connection device for the wheel of a motor vehicle, comprising a wheel hub carrier equipped with the aforementioned means of articulation, characterized in that a first connecting piece is secured to the wheel hub carrier, while the second connecting piece is secured to a suspension wishbone connecting to the body of the vehicle, the first axis of rotation extending approximately in a vertical direction and the second axis of rotation extending approximately in the longitudinal direction of the vehicle.
Provision may be made for the articulation yoke borne by the piece for connecting to the wishbone to be mounted in this piece with the interposition of axial stops, it being possible for each axial stop to have a number of thicknesses of elastomer separated by a number of intermediate flat rings made of a non-elastomeric material; in this case, the non-elastomeric material is advantageously chosen from the group consisting of metal leaf or foil, wovens, nonwovens, thermoplastics and thermosets. The axial stops may be mounted in the piece for connecting to the wishbone, one on each side of the shoulders which form the transition between the journals and the central part of the yoke; they are advantageously mounted with preload approximately in the longitudinal direction of the vehicle; each axial stop is preferably a laminated elastomer assembly containing annular separations made of non-elastomeric material. This axial stop can be used, in particular, when the invention is applied to the articulation between the hub carrier and the lower arm of a Mac Pherson-type suspension. A stop of this kind is not, however, of use in the application of the invention between the hub carrier and the steering linkage.
In one alternative form, the connection with the ground is of the double wishbone suspension type, in which the second suspension wishbone is connected to the wheel hub carrier by a means of articulation according to the invention.
In another alternative form, the ground connection is of the Mac Pherson type and includes a strut mounted between the hub carrier of the wheel and the body of the vehicle, and a coil spring mounted between a lower spring plate secured to the body of the strut and an upper spring plate secured to the rod of the strut, the upper spring plate being secured to a laminated elastomer assembly secured to a piece for attaching to the body of the vehicle, preferably a vehicle suspension tower.
In the case of a ground connection of this type, the piece for attaching to the body of the vehicle may be shaped as a convex cup tailored to the interior surface of the suspension tower; the piece for attaching to the body may be angularly adjustable with respect to said piece; the upper end of the coil spring may be angularly indexed by insertion in a part of the upper spring plate, which is advantageously overmolded with an elastomeric material, at least in the region against which the spring bears.
According to a first alternative form, the attachment piece is mounted so that it can pivot with respect to the body via a rotation-adjustment lever.
According to another alternative form, the attachment piece and the body each have a number of orifices located on circles of one and the same diameter and spaced apart in such a way as to allow angular indexing at the time of mechanical assembly of the piece for attachment to the body and the body.
According to another alternative form, the body has a number of first shapings and the piece for attachment to the body has a number of second shapings, and a first shaping belonging to the body collaborates with a second shaping belonging to the piece for attaching to the body, so as to provide indexing between the body and the piece for attaching to the body.
Advantageously, the piece for attaching to the body has a radially interior part collaborating with a relaxation stop to prevent the strut from disengaging if the vehicle wheel should lift off the ground and the laminated elastomeric assembly should break; the radially interior part may be coated at least partially or overmolded with a shock-damping material.
Provision may be made for the piece for attaching to the body to be shaped in such a way that it clips into the body.
By virtue of the special arrangements just described, it is possible to dispense with the upper thrust ball bearing which is usually present in a Mac Pherson-type ground connection and this can be replaced by an elastic system, the operating torque of which is approximately proportional to the angle of pivoting. An elastic system of this kind may be produced in modular form, to allow an interchangeable modular unit comprising a strut and an associated spring to be factory assembled; this system also allows the torsion of this interchangeable unit to be preadjusted following assembly with the body of the vehicle, so as to compensate for any lateral loading or any torque which might be due to the tire and to the running conditions (camber).
The invention is also aimed at a ground connection device characterized in that the wheel hub carrier is connected by two means of articulation to, respectively, the steering linkage and to the suspension wishbone, as mentioned hereinabove.
To allow better understanding of the subject-matter of the invention, a number of embodiments thereof will now be described by way of illustrative and nonlimiting example, with reference to the appended drawing.